Sliding bearing element with lubricating oil pockets

ABSTRACT

Plain bearing elements comprise at least one single-layer metallic bearing material (4) having a sliding surface (6) with lubricating oil pockets (10). The depth (T) of the open oil pockets (10) is 0.03 mm to 0.3 mm, and the ratio of the pocket area to the pocket depth is 10 to 40 mm. The plain bearing elements exhibit superior running qualities and properties. The depth of the oil pockets (10) may be adapted to the service viscosity of the lubricating oil. The oil pockets (10) in the same plain bearing element may also have varying depths (T) and be provided only in predetermined regions of the plain bearing element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a plain bearing element comprising asingle-layer or multilayer metallic bearing material, pockets forlubricating oil being provided in the sliding surface. The term "plainbearing elements" is intended to mean, among others, plain bearinghalf-liners, flanged bearings, bushes and thrust washers, comprising asingle-layer or multilayer metallic bearing material which may bedeposited on a backing material.

2. Description of Related Art

Provision of depressions on the sliding surface has been known foryears. It is suggested in DE-PS 546 781 to make, for the avoidance of"contact oxidation", in one of the contacting surfaces of a bearingdiscontinuities, depressions, roughenings and similar means. In thisconnection also circular depressions were shown but it is not stated howthese depressions are dimensioned, arranged or lined.

DE-PS 834 480 describes a bearing in which the bearing surface iscomposed of a plurality of small areas of hard and soft bearingmaterial. Apart from groove-shaped depressions also square-shapedrecesses are provided which are, however, completely filled with a softbearing material. The depressions are made by means of an embossing rollrotating in a metallic bath.

From DE-OS 27 11 983 is known a bearing which has, in addition to oilgrooves, also hemispherical oil recesses of a diameter of 1.5 to 2.5 mmwhich are arranged with a spacing of 4 mm in circumferential directionor 4.8 mm in axial direction. Because the thickness of the bearing alloyis only 0.25 mm these oil recesses extend up to the steel backing. Thelubricating oil pockets of these dimensions have, among others, thedisadvantage that the bonding region of the bearing alloy with the steelbacking is exposed so that delaminations may occur in this region.

From DE 33 26 316 C2 are known bearing bushes of sintered metal withlubricating oil pockets arranged on the inner sliding surface, thepockets being hemispherical or ellipsoidal. The depth of the oil pocketsis 0.2 to 1 mm while 10 to 30% of the entire sliding surface is occupiedby the oil pockets.

AU 143 992 shows a sliding surface design with embossed recesses whichare entirely filled with a soft plain bearing material.

DE-GM 7817118 describes self-lubricating bearing which has for theembedding of a solid lubricant cavities of circular or spherical shape.

From U.S. Pat. No. 5,462,362 is known a sliding element used forextremely low sliding velocities such as spherical elements inartificial joints. The sliding surface has cylindrical recesses whosediameter is 0.2 to 0.8 mm and depth is 1 to 10 μm. The recesses are alsofilled with a solid lubricant.

These known bearing elements may be used, depending on the bearingmaterial, only for low sliding velocities of up to about 5 m/s andaverage loading of up to about 30 MPa. The bearing elements are notsuitable for use as big-end bearings and main bearings ininternal-combustion engines because due to the relatively large depthand/or the large area occupied by the oil pockets the build up of thehydrodynamic pressure needed for these applications is not possible to asufficient degree.

Also known are bearing elements according to EP-PS 104159 and U.S. Pat.No. 5,238,311 which have groove-shaped recesses in the sliding surfacewhose depth is 3 to 6 μm. These elements have the disadvantage that whenthe grooves are subjected to the loadings of over 30 MPa which is commonin big-end bearings and main bearings of internal-combustion engines,they are either plastically deformed or worn which may lead to seizureso that they may no longer perform their task.

The groove bearings described in EP-PS 57808 which comprise groovesfilled with soft bearing materials have, in practice, the disadvantagethat after a certain time of operation the soft bearing material ifflushed out by the lubricating oil and the bearing is no longer able tofunction.

SUMMARY OF THE INVENTION

It is therefore the aim of the invention to improve sliding elementswith lubricating oil pockets to such an extent that their runningqualities are better than those of known plain bearing elements with oilpockets and that their properties are superior to those of both thebearings with open and with filled grooves and the bearings without oilpockets.

A large number of experiments with lubricating oil pockets of variousshapes known from the state of the art, brought no significantimprovement of performance in service, so that no advantage could beexpected from the selection of dimensions. Because oil pockets generallyreduce the proportion of supporting surfaces, oil pockets mustconsequently be considered as disadvantageous.

It was therefore that much more surprising to find that plain bearingelements whose oil pockets have a small depth of 0.03 mm to 0.3 mm andin which the ratio of the pocket area to the pocket depth is 10-40 mmexhibit an outstanding performance in service, for instance in serviceconditions common for big-end bearings and main bearings ofinternal-combustion engines when using conventional lubricants such asengine oils according to SAE. The lubricating oil pockets becomecompletely filled with lubricant only when these dimensions areobserved, so that, in operation, a hydrodynamic pressure may obviouslybe built up with respect to the element in sliding contact in connectionwith the closely delimited pocket which is closed on all sides except inthe sliding surface, this pressure being the same as that at the smoothsliding surface and consequently contribution to the share in supportingis surprisingly made.

In any case the pocket depth must be smaller than the thickness of thelayer of bearing material in which the oil pockets are made.

This dimensioning of the oil pockets applies preferably for bearingelements where the diameter of the bearing is 35 to 160 mm. The depth ofthe oil pockets is preferably of the order of the clearance between theelements in sliding contact.

The loading is taken up not only by the supporting surfaces between theoil pockets but also by the lubricant in the oil pockets, so that theoil pockets do not serve only for the supply of lubricant as in thestate of the art. As a consequence sliding velocities greater than 20m/s and loading of over 50 MPa may be used for aluminium alloys and morethan 70 MPa for bronzes with electroplated layers may be used withoutany problem. Also antiseizure properties are improved, because even whenthe supporting surfaces are running dry the lubricant in the pocketscontributes to hydrodynamic support. Further, even frictional losses aresignificantly reduced.

Also in comparison with bearings with open grooves not filled with softbearing material (U.S. Pat. No. 4,538,929) the plain bearing elementsaccording to the invention are superior in that the lubricant in the oilpockets cannot escape in circumferential direction as in the case ofgrooves, but is accumulated in the oil pockets and inflow and outflow ofthe lubricant takes place only across the thin lubrication gap. Inaddition to the hydrodynamic pressure also a pressure component developsdue to the diffuser action on inflow of the lubricant into the oilpocket while on the outflow a pressure component is produced by thedamming-up edge.

The properties of the plain bearing elements may be further optimizedwhen the relationship between the dimensioning of the oil pockets andthe viscosity of the used lubricants is taken into consideration. Thedepth of oil pockets in bearings for internal-combustion engines shouldpreferably be T=0.5 to T=e^(a), where a=0.45·lnη-3 and T is in mm, whenthe dynamic viscosity η of the lubricant at service temperature is givenin mPas. The equation applies to operational viscosities of η=1.8 mPasto 50 mPas which corresponds to the use of conventional engine oils attemperatures of about 60° to 180° (0. .R Lang, W. Steinhilper"Gleitlager", 1978, Springer-Verlag, p. 36).

The area of all the oil pockets together should preferably not exceed10% of the whole area of the sliding surface of the plain bearingelement, because otherwise the proportion of the area of the undisturbedsupport surfaces would be too small to withstand the high loading inmodern internal-combustion engines.

All the oil pockets need not necessarily have the same depth. On thecontrary, it may be advisable for special applications to select thedepth of the oil pockets in the region of highest loading or smallestthicknesses of the lubricating film in order to improve the supply oflubricant, and to continually reduce the depth of the oil pocketstowards the region of increasing thicknesses of the lubricating film.Particularly, in the case of big-end bearings and main bearings theirareas exposed to highest loading and most endangered by wear are known,so that a tailor-made plain bearing element may be provided.

In the case of inadequate lubrication also the reverse case may beadvantageous i.e the deeper oil pockets are arranged in areas which arenot loaded to provide thereby an additional oil reservoir.

The oil pockets are preferably embossed in the bearing material. Themachining is preferably carried out on a strip. This is much simplerthan making grooves in a bearing liner that has already been formed.After the embossing of the oil pockets the strip-shaped material issubjected to forming and finally processed in the sliding surface.

So as to achieve good loadability, the bearing material in which the oilpockets are made is preferably a relatively hard alloy based onaluminium or copper. Such bearing materials can be exposed to high loadsand have the advantage that they may be deposited directly onto thesteel backing. Due to the relatively high tendency of such hard bearingmaterials to seizure, these materials could, until now, be used withoutadditional overlay only for low sliding velocities. In order to counterthe tendency to seize, experiments were made in the past to add, apartfrom additional coating, more tin or lead to the alloys. It was foundthat by the provision of oil pockets according to the invention theaddition of these soft materials can be largely dispensed with. It wasfound further, that plain bearing elements with these bearing alloys maybe used not only for higher sliding velocities but also for higherloading. On top of this also the antiseizure properties of the materialcould be significantly improved by the special design of the oilpockets.

According to a further embodiment, the sliding surface of the bearingmaterial in which the pockets are made is additionally coated with anelectroplated layer or a sputtered layer whose thickness is much smallerthan the thickness of the oil pockets. Such a coating may be made on anybearing materials, but preferably on lead bronze.

The oil pockets are preferably not entirely filled with theelectroplated layer or a sputtered layer. On the contrary, thedepressions in the sliding surface are retained. Because theelectroplated layer or sputtered layer form a continuous coating, acontinuous coating between the supporting surfaces and the areas of theoil pockets are achieved independently of the shape of the oil pockets.Frayed portions on the margin of the oil pockets, which could be causedby the embossing of the bearing material or by the cutting of thesliding surface, are coated and evened out by the electroplated layer orsputtered layer.

The thickness of the electroplated or sputtered layer may be greaterthan the depth T of the oil pockets when it is ensured that the outlineof the electroplated or sputtered layer follows the outline of the oilpockets made in the layer of bearing metal.

For instance the following bearing alloys may be used:

AlNi2MnCu, AlZn5SiCuPbMg, AlSn6, CuPb22Sn, CuPb17Sn5, CuPb10Sn10 orCuPb22Sn3. Preferred electroplated layers consist of PbSn10Cu2,PbSn10Cu5, PbSn14Cu8 on an intermediate layer of Ni, or possibly on anintermediate layer of NiSn. A preferred sputtered layer is AlSn20.

Any shape of the oil pockets may be chosen; it has been found, however,that it is advantageous when the oil pockets have either the shape of aspherical segment or a frustum of a cone. The side-wall angle of thefrustoconical oil pockets should be in the region of between 30° and60°, preferably 45°. The inclination of the sidewalls may be used toadjust the proportion of lubricant which is forced by the movement ofthe elements in sliding contact from the oil pockets onto the supportingface portion. Because the advantage of the oil pockets is in that apressure is built also in the region of the oil pockets, it was the aimat high loading to force, in operation, from the oil pockets as far aspossible only small quantities of lubricating oil. If, on the otherhand, the aim is to improve primarily the antiseizure properties,greater angles are preferred. Consequently smaller angles from the rangeof 30° to 60° are preferred for the sidewall angle α.

According to another embodiment the oil pockets may have in top view theshape of rhombuses.

The plain bearing element is preferably a plain bearing half-liner. Inthis embodiment the oil pockets are arranged preferably one afteranother in lines transverse to the circumferential direction and thecircumferential lines make with the circumferential direction any angleβ, preferably between 15° and 40°. The linear arrangement correspondsapproximately to the arrangement of grooves in grooved bearings, but theangle β is greater.

The oil pockets are arranged one after another in lines which arepreferably also transverse to the axial direction and the transverselines make with the axial direction of the bearing liner any angle γ,preferably between 5° and 25°. In view of the angles β and γ, thelongitudinal lines and the transverse lines form a rhombus-shapedpattern.

It was found that this arrangement of oil pockets is more advantageousbecause otherwise a shadow effect is produced, which causes that not alloil pockets, particularly if arranged closely one after another,contribute to the improvement of the running qualities of the plainbearing liner and may even have a negative effect.

An arrangement of oil pockets one after another is not disadvantageousif the spacing of oil pockets which are adjacent in the direction ofsliding, i.e. in the case of liners and bushes in circumferentialdirection, is at least 12 mm.

According to the purpose of use the oil pockets may be limited to thecrown area and to a region of circumferential angles δ of the plainbearing liner or bush of ±30° to ±60° around the crown area.

Plain bearing elements according to the invention are suitableparticularly for main and big-end bearings for piston engines,particularly internal combustion engines, which is not the case withconventional sliding elements with open depressions.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,in greater detail with reference to the drawings, in which:

FIG. 1 is a perspective representation of plain bearing half-linersaccording to a first embodiment,

FIG. 2 is a perspective representation of a bearing bush,

FIG. 3 is a section along line III--III in the plain bearing half-linershown in FIG. 1,

FIGS. 4A,B is a section along line IV--IV through the plain bearinghalf-liner shown in FIG. 1 for two different embodiments,

FIG. 5 is a perspective representation of a plain bearing half-lineraccording to a further embodiment,

FIG. 6A is a section along line VIa--VIa in the plain bearing half-linershown in FIG. 1,

FIG. 6B is a section along line VIb--VIb in the plain bearing half-linershown in FIG. 5,

FIGS. 7A,B are top views of the developed sliding surface of the plainbearing half-liner shown in FIG. 1 for two different embodiments,

FIG. 8 is a perspective representation of a flanged bearing,

FIG. 9 is a diagram in which are plotted rotational frequencies in thecase of inadequate lubrication, and

FIG. 10 is a diagram for sliding performance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 are shown, in perspective representation, plain bearinghalf-liners 1 which bear onto each other at their parting line surfaces9 and form, for instance, a main or big-end bearing, and in FIG. 2 isshown, in perspective representation, a bearing bush 2. On the steelbackings 3 is, in both cases, deposited, for instance, an aluminiumalloy 4,4'.

Into the surface of the aluminium alloy 4,4' which forms the respectivesliding surface 6,6' of the plain bearing half-liner 1 or the bearingbush 2, are embossed cap-shaped depressions which form lubricating oilpockets 10, 10'. In the embodiments shown in FIGS. 1 and 2, the oilpockets 10,10' are uniformly distributed over the whole sliding surface6,6' of the plain bearing half-liner 1 or the bearing bush 2.

In FIG. 3 is shown a section along line III--III through the half-liner1 shown in FIG. 1. As can be seen, the oil pockets 10 have the shape ofa spherical segment whose diameter D is much greater than the depth T ofthe oil pockets 10 (see FIG. 6A) measured from the sliding surface 6.The oil pockets 10 are fully contained in the respective plain bearingmaterial, i.e. T is smaller than the thickness of the aluminium layer 4.The diameters D of the oil pockets 10 may be in the region of about 0.5mm to 3.5 mm and the depth T may be at the most 0.3 mm and at least 0.03mm, while only such diameter and depth values may be combined, that theratio of the pocket area to the pocket depth is 10 to 40 mm. Inprinciple any geometrical shape is possible as is shown, for instance,in FIG. 7B.

The arrangement and shape of the oil pockets 10' of the bearing bush 2corresponds to those shown in FIG. 1.

In FIGS. 4A,B is illustrated a section along line IV--IV through theplain bearing half-liner 1 shown in FIG. 1 for two embodiments. The oilpockets are of different depths; the depth in the embodiment shown inFIG. 4A is continuously decreasing from the crown area 8 to the partingline surfaces 9. The oil pockets 10a in the region of the parting linesurfaces have only about half the depth of the oil pockets 10c in theregion of the crown area 8 of the plain bearing half-liner 1. The oilpockets 10b in the transitional region have, on the contrary, a depthwhich lies approximately between that of the oil pockets 10c and the oilpockets 10a. The section IV--IV in FIG. 4B shows oil pockets 10a', 10b',10c' whose depth is in reverse arrangement compared to FIG. 4A. As isapparent, the oil pockets 10c' in the crown area 8 have the smallestdepth in the crown area 8, while the depth of the oil pockets 10b' and10a' increases towards the parting line surfaces 9.

The arrangement and shape of the oil pockets 10a,b,c or 10a',b',c' istransferable to the bearing bush 2 shown in FIG. 2.

In FIG. 5 is shown a further embodiment of a plain bearing half-liner 1in which the oil pockets 10" are provided only in a region ofcircumferential angle δ=±45° in the region of the crown area 8. This isthe region of the greatest loading of the bearing or the smallestthickness of the lubrication film. The design of the plain bearinghalf-liner 1 in FIG. 5 differs from that in FIG. 1 in that first a leadbronze 4a is deposited on the steel backing 3 and the former is fullycoated with an electroplated layer 5 or a sputtered layer.

FIG. 6A shows, in a section VIa--VIa through the plain bearinghalf-liner 1 according to FIG. 1, oil pockets 10 in the shape of aspherical segment.

FIG. 6B shows, in a section VIb--VIb through the plain bearinghalf-liner 1 according to FIG. 5, frustoconical oil pockets 10" whosesidewalls 11 make with the perpendicular an angle α of about 45°. Theoil pockets 10" are embossed in the lead bronze 4a and the electroplatedlayer 5 has everywhere the same thickness d, even in the region of theoil pockets. The oil pockets 10" are therefore fully lined but have thesame depth as they had before electroplating, while the thickness d ofthe electroplated layer 5 is smaller than the depth T of the oil pockets10" embossed in the lead bronze 4a which, however, need not be so inprinciple. It must be ensured that the oil pockets are, as before, opento admit lubricating oil.

FIG. 7A is the top view of a developed sliding surface 6 of the plainbearing half- liner 1 shown in FIG. 1. The oil pockets 10 are arrangedone after another in longitudinal lines 15, and the longitudinal lines15 make with the circumferential direction 17 an angle β which is about30°. The oil pockets are also arranged in transverse lines 16 which makewith the axial direction 18 an angle γ of 15°. This angular arrangementensures that the spacing of the oil pockets in the circumferentialdirection 17 is at least 12 mm.

FIG. 7B shows, in a manner similar to FIG. 7A, the development of asliding surface 6 with oil pockets 10"' which are rhombus-shaped in topview.

FIG. 8 shows in perspective representation a flanged bearing 19. As isapparent, also the flanges 20 are provided with lubricating oil pockets21 and the arrangement and shape of the oil pockets 21 is comparable tothe earlier described oil pockets.

FIGS. 9 and 10 show comparative tests.

In FIG. 9 is plotted the maximum rotational frequency which in the caseof inadequate lubrication reaches seizure in the case of plain bearingsboth with and without oil pockets. Tested were bearing liners of steelwith a bearing alloy of lead bronze with an electroplated layer. Thebearing liner with oil pockets had the following specification:

Pocket depth: 0.08 mm

Ratio of pocket area to pocket depth: 22 mm

Total area of all oil pockets: 45 mm² ≈3% of the total sliding surface

β: 21°

γ: 10°

In this test the oil pockets were uniformly distributed on the wholesliding surface and all the oil pockets have the same depth T. Theviscosity of the lubricating oil was η=3 mPas.

The diagram in FIG. 9 shows that, in the case of inadequate lubrication,a bearing according to the invention can rotate at a much higherrotational frequency before seizure occurs.

In the bar diagram in FIG. 10 is shown the sliding performance ofbearing liners of steel with an overlay of an aluminium alloy based on15 tests with plain bearing liners without oil pockets. In all bearingliners seizure occurred at the most after 10 h. Also 10 tests with plainbearing liners of the same alloy but with oil pockets were made at anincreased rotational frequency, of which nine tests lasted for 200 h andone test for over 500 h. All tests were stopped on reaching the testtime without damage. The shape of the oil pockets was the same as in thetest according to FIG. 9.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is, therefore, tobe understood that within the scope of the appended claims, whereinreference numerals are for convenience and not to be considered in anyway limiting, the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. A plain bearing comprising:a metallic backing; ametallic bearing layer of bearing metal applied to said backing; and aplurality of lubricating oil-retaining pockets provided in said bearinglayer having depths of about 0.03 mm to 0.3 mm and ratios of pocket areato pocket depth of about 10 to 40 mm.
 2. The plain bearing of claim 1including a sliding surface of predetermined area and wherein saidpockets have a combined area ≦10% of said sliding surface area.
 3. Theplain bearing of claim 1 wherein said pockets have varying depths. 4.The plain bearing of claim 3 wherein said pockets have the greatestdepth in regions corresponding to highest loading or least thickness ofthe lubricating oil and continuously decrease in depth toward regionscorresponding to lowest loading or greatest thickness of the lubricatingoil.
 5. The plain bearing of claim 3 wherein said pockets have thegreatest depth in regions corresponding to lowest loading andcontinuously decrease in depth toward regions corresponding to highestloading.
 6. The plain bearing of claim 1 wherein said pockets comprisesembossed indentations extending into said bearing layer.
 7. The plainbearing of claim 1 wherein said bearing metal comprises an aluminumalloy.
 8. The plain bearing of claim 1 including a covering layerapplied to said sliding surface and said pockets.
 9. The plain bearingof claim 8 wherein said covering layer is selected from a groupconsisting essentially of an electroplated layer and a sputtered layer.10. The plain bearing of claim 8 wherein said covering layer has apredetermined thickness relatively less than said depth of said pockets.11. The plain bearing of claim 8 wherein said covering layer has apredetermined thickness relatively greater than said depth of saidpockets and applied uniformly across said pockets so as to retain thepresence of said pockets in said covering layer.
 12. The plain bearingof claim 1 wherein said pockets have a predetermined shape.
 13. Theplain bearing of claim 12 wherein said predetermined shape comprises aspherical segment.
 14. The plain bearing of claim 12 wherein saidpockets are frustoconical in shape.
 15. The plain bearing of claim 14wherein said frustoconical pockets have a predetermined side-wall anglein the range of about 30° to 60°.
 16. The plain bearing of claim 12wherein said predetermined shape of said pockets comprises a rhombuswhen viewed in plan.
 17. The plain bearing of claim 1 wherein saidpockets are arranged in succession in longitudinally extending linesmaking an angle β of about 15 to 40° with respect to a circumferentialdirection of said bearing.
 18. The plain bearing of claim 17 whereinsaid pockets are further arranged in transversely extending lines makingan angle γ with an axial direction of said bearing.
 19. The plainbearing of claim 1 wherein said pockets are arranged in a grid patternextending in succession along longitudinal and transverse lines andspaced from one another in a direction of sliding by a distance of atleast 12 mm.
 20. The plain bearing of claim 1 including a crown area ofsaid bearing extending across a circumferential angle of about ±30° to60° and wherein said pockets are provided in said crown area only. 21.The plain bearing of claim 1 wherein said bearing comprises a mainbearing of an internal combustion engine.
 22. The plain bearing of claim1 wherein said bearing comprises a big end bearing of an internalcombustion engine.
 23. In an internal combustion engine including atleast one plain bearing selected from the group consisting essentiallyof main bearings and big end bearings having a construction,comprising:a metallic backing; a metallic bearing layer of bearing metalapplied to said backing; and a plurality of lubricating oil-retainingpockets provided in said bearing layer having depths of about 0.03 mm to0.3 mm and ratios of pocket area to pocket depth of about 10 to 40 mm.